The present invention relates to a consumable electrode type arc welding power source. More particularly, the invention relates to a power source for a consumable electrode type arc welding machine for short-circuit transfer welding with a switching element, e.g. a transistor, as a primary welding current control element.
With a conventional arc welding power source operated by a DC voltage, desired welding characteristics are obtained by connecting a reactor 1 having an inductance component L to a primary welding current branch circuit as shown in FIG. 1 and suitably selecting the value of the inductance L of the element. In FIG. 1, reference numeral 2 designates a DC power source. When a welding operation is carried out by short-circuit transfer welding in this case, a load voltage U will vary as shown in FIG. 2A and the welding current will vary as shown in FIG. 2B. Assuming that a no-load voltage of the DC power source 2 is designated by E, the rate of current increase becomes substantially dI/dt=E/L. In FIGS. 2A and 2B, the period A is a time duration during which a short-circuit current flows from a wire electrode to a base material to be welded. The short-circuit current is gradually increased, while the increase in the short-circuit current is restricted by the reactor 1, during the period A until the molten portion of the wire electrode is then separated and transferred from the short-circuit state to the separated arc generating state by an electromagnetic pinch strength which increases with respect to the vibration of the molten portion of the wire electrode on the base material. The period B is a time duration during which an arc is produced so that the end of the wire electrode deposited on the base material is heated to a high temperature and is molten together with the base material due to the heat of the arc. Thus, in the short-circuit transfer welding, the short-circuit period A is the time interval during which the molten portion of the wire electrode is transferred to the base material to be welded and the arc producing period B is the time interval during which the transferred end of the wire electrode and the base material are heated and molten. When such two periods are repeated, the short-circuit transfer welding can be effected. The length of the arc production period is determined by the value of the inductance and the value of the no-load voltage E, and the ratio of the short-circuit period to the arc production period is determined only by the value of the inductance.
The characteristics of the arc welding power source the above described short-circuit period and the arc producing period are important factors in determining the amount of spatter due to the short-circuit welding, the penetration depth and so forth. In order to adjust the characteristics in a variety of states, it is necessary to connect reactors 1 having various inductance values or to control the power source output voltage to various values, neither of which procedures is easy. Particularly, it is very difficult to switch the various reactors 1. Further, in case of large current, it is difficult to adjust the reactors, and it is also necessary to employ considerably expensive elements for the reactors 1 due to their large size.